1. Field of Invention
The present invention relates to a driving method of a liquid crystal display. More particularly, the present invention relates to a driving method capable of both retaining sharp imagery and saving power consumption.
2. Description of Related Art
As semiconductor devices and human machine display proceed, multi-media industry makes progress significantly. As to display device, a Cathode Ray Tube, CRT, display has monopolized the display device market for years for its superior display quality and its economical characteristic. However, as multi-terminal/display personal station is popular and as environmental issue is in demand, a CRT display is still under dispute for spatial usage and energy consumption reasons. It is apparent that a CRT display does not meet low power requirement and the demand of lightness, thinness, shortness and handiness. Thus a sharp imagery, space efficient, low power consumption, and radiation-free display, i.e. a liquid crystal display, LCD, is taking the lead.
A LCD image is composed of an array of pixels, and the brightness of each pixel is driven by the brightness of the back-light module as well as a grayscale value of the pixel. The present common driving method is to operate the back-light module at a constant brightness, and manipulate the bias voltage to twist each liquid crystal of the pixel; the phases of nematics of the liquid crystal thus determine light transmittance in order to display grayscale.
FIG. 1 illustrates a profile showing light transmittance of a pixel vs. bias voltage. Referring to FIG. 1, each pixel of a LCD is attacked by poor grayscale display. This poor performance is usually considerable in bright image (high grayscale) and, particularly, in dark image (low grayscale) regions. Besides, there is similar performance in higher light transmittance region, yet human eyes are less sensitive to grayscale when exposing to higher brightness.
When a LCD displays in the dark image region, the light transmittance of a liquid crystal molecule varies insignificantly as opposed to other display regions for the physical characteristic per se. Therefore, when the maximal brightness of an image is low, i.e. located in low grayscale display region, the available grayscale values are apparently not sufficient to display the entire image, and poor image quality is thus incurred.